A battery-powered acoustic device intended to compensate for impaired hearing by transmitting amplified sound waves to the eardrum through air. It typically consists of a microphone, an amplifier, and a speaker (receiver) contained in a case worn behind-the-ear (BTE). The microphone receives sound waves and converts them into electrical signals which are increased by the amplifier and sent as sound waves, by the speaker, to the eardrum through an earmould that fits inside the outer ear or a tube in the ear canal. The device is used for mild to profound hearing loss; most types are programmable to enable computerized adjustments for a patient's hearing loss and related factors.